Paging systems are a reliable and generally inexpensive communication tool. Paging systems operate on a variety of communication protocols, including the FLEX® protocol by Motorola Inc., which is a four-level protocol that presently functions at bit rates of up to sixty-four hundred bits per second. Generally, the FLEX® protocol reduces the number of errors received in transmissions and reduces the possibility that a page will be missed or garbled to the point where it is unreadable or unusable. Further, it allows for a relatively large number of end users to be supported.
The modulation range of FLEX® is plus and minus forty-eight hundred kilohertz of deviation. FLEX®'s four levels are defined as −4,800 hertz, −1,600 hertz, +1,600 hertz, and +4,800 hertz, with reference to the operating frequency. Each level represents two bits in a given transmission. They represent ‘00’, ‘01’, ‘11’, and ‘10’ respectively.
Additionally, FLEX® allows for the adjustment of bit rate based upon the channel loading, operating at 1,600, 3,200, or 6,400 bits per second. FLEX® can switch between four level and two level operation as needed, which can improve paging quality during times of low or reduced activity and increase channel capacity during times of high traffic.